Replace confusing member variable with a predicate

The Converter class, in the eponymous example, had a null member
variable that wasn't a nullptr - it pointed to an instance of
NullConverter - so that other converters could test whether a
Converter * they'd been passed was null (in the sense of pointing to a
NullConverter). This, however, was susceptible to misreading - I
misread one such comparison as a nullptr check and thus thought it
redundant with an earlier actual nullptr check. To spare future
readers similar confusion, replace the public static member variable
with a protected (since only other derived classes need it) static
predicate, to at least give the reader a clue that this is using the
word null in a class-specific sense.

Pick-to: 6.6 6.5
Task-number: QTBUG-111228
Change-Id: I1e4f494b303d1bf90107f8c6fa3a4a22f6d81b90
Reviewed-by: Thiago Macieira <thiago.macieira@intel.com>

1 files changed, 4 insertions, 1 deletions

diff --git a/examples/corelib/serialization/convert/nullconverter.cpp b/examples/corelib/serialization/convert/nullconverter.cpp
index 7c499efd73..00ae47a086 100644
--- a/examples/corelib/serialization/convert/nullconverter.cpp
+++ b/examples/corelib/serialization/convert/nullconverter.cpp
@@ -6,7 +6,10 @@
 using namespace Qt::StringLiterals;
 
 static NullConverter nullConverter;
-Converter *Converter::null = &nullConverter;
+bool Converter::isNull(const Converter *converter)
+{
+    return converter == &nullConverter;
+}
 
 QString NullConverter::name() const
 {